Weltstadthaus

Glass skin

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Flowing, transparent, anatomical – this is how the “Weltstadthaus” designed by Renzo Piano fits into the corner of Antonsgasse and Schildergasse in Cologne city centre. With his modern design, the star architect pushes the “blob” style of architecture forwards. The organically formed building has a harmonizing effect on the pulsating shopping district. The idiosyncratic jacket of the building, made of glass and wood, is both architectural vision and technical challenge. In order to combine this extraordinary shape with a high degree of functionality, the planners developed an elaborate façade construction – jacketed with ipasol natura 67/34 (Interpane). Photo: Erika Koch for Peek & Cloppenburg KG Düsseldorf

“Architecture at the highest international level” was the demand of the client Peek & Cloppenburg on their “Weltstadthaus” buildings. Renzo Piano has now realized his ideas of a shopping palace in Cologne under difficult urban development conditions. Wedged between a busy shopping district and an arterial road with heavy traffic, surrounded by concrete façades from the seventies and in the neighbourhood of a late Gothic church, his idiosyncratic design of glass and wood flows into place.

A “sleeping whale”

The building, optically split in two, appears like a glass whale winding around a cliff. The glass house, which is 130 metres long and up to 34 metres high is reminiscent of a 19th century orangery. The architect describes his design as "A modern building with, however, a clear reference to tradition, through the use of wooden arches and glass”. The foundation of the department store with a floor space of 22,000 square metres is a reinforced concrete construction. On top of this foundation rests a wooden construction which supports and shapes the glass jacket composed of round and elliptical profiles.

On wooden ribs

At the level of the fourth story the supporting framework for the roof and façade construction rests vertically on the reinforced concrete skeleton. 66 timber girders are connected like ribs to the steel ridge girder, the three-dimensional, slightly curved, “backbone” of the body. The glue-laminated girders are made of 60 millimetre thick and 160 to 220 millimetre wide lamellae of Siberian larch. Only every fourth to sixth of these wooden ribs rests directly on the skeleton. In between, the façade is a self-supporting construction.

Nestled into the curves

The glass lightly and delicately encases the designer shops. It was not easy to realize these soft shapes: A “scaled” façade of modular stepped glazing units was created. Nearly everyone of the almost 7,000 inserted glass panes is unique – the individual façade segments vary in angles and dimensions. The CNC controlled glass cutting makes it possible to follow the soft lines of the body. In order to fully realize the architectural curves of the design the insulating glazing elements were slightly cold-forged after insertion. This generated an optically and functionally sophisticated building jacket which combines high transparency with a comfortable indoor climate.

Showing real colours

Shopping under ideal conditions – the solar control glazing ipasol natura 67/34 (Interpane) fulfils the special demands of a trend setting department store: Rooms flooded with daylight (tL= 67%) and true colour presentation of apparel and accessories. Particularly important for a relaxing shopping expedition: A balanced relation of solar protection in the summer and thermal insulation in the winter. With a low solar factor of 37 percent (EN 410) and excellent thermal insulation (1,1 W/m²K as per EN 673), the "glass skin" made of ipasol natura 67/34 controls the temperature. In addition, the ground floor of the building comprises approximately 1,000 square metres of thermal insulating glazing (iplus by Interpane).

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Since 7 September, the glass “blob” in the centre of Cologne has been attracting shoppers. Under a 4,900 square metre glass façade, Renzo Piano has created sophisticated shopping possibilities. Photo: Andreas Fechner for Peek & Cloppenburg KG Düsseldorf

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A “glass whale”, stranded in downtown Cologne. Surrounded by concrete façades from the 70's, the department store has reinvented its surroundings and created a new space in front of the Antoniterkirche. Photo: Andreas Fechner for Peek & Cloppenburg KG Düsseldorf

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Wood and glass design – thanks to ipasol natura 67/34 (Interpane) the building jacket fulfils the optical criteria as well as the functional demands on a department store: comfortable temperatures and true colour representation. Photo: Erika Koch for Peek & Cloppenburg KG Düsseldorf